1. Field of the Invention
This invention relates to flame retardant resin compositions based on synthetic resins containing an aromatic ring in a molecule such as aromatic polycarbonate resins and aromatic epoxy resins.
2. Prior Art
Flame retardant resin compositions are often used in various products such as electric and electronic parts, building members, automotive parts, and daily goods. These resin compositions are generally made flame retardant by adding organic halogen compounds optionally in admixture with antimony trioxide. However, these flame retardant resin compositions have the drawback that harmful halogen gases evolve upon combustion.
It is also known that resin compositions can be made flame retardant by adding silicone resins which do not evolve harmful gases.
JP-A 36365/1979 discloses a flame retardant resin composition wherein a silicon resin containing at least 80% by weight of trifunctional siloxane units is added to an organic resin. With respect to the organic resin, no reference is made to aromatic polycarbonate resins and aromatic epoxy resins. With a focus on the melt processing of the organic resin, a relatively high molecular weight silicone resin substantially free of crosslinking functional radicals and having a softening point above room temperature is selected. On account of a relatively weak flame retardant effect, the silicone resin must be added in a large amount of about 10 to 300 parts by weight per 100 parts by weight of the organic resin, detracting from the properties of the organic resin.
JP-A 500780/1983, 226159/1992, and 33971/1995 disclose flame retardant resin compositions having added thereto silicone resins consisting of monofunctional siloxane units and tetrafunctional siloxane units. JP-A 128434/1994 discloses a flame retardant resin composition having added thereto a silicone resin containing vinyl-bearing siloxane units. In order to exert satisfactory flame retardant effect, all these compositions, however, require to increase the amount of silicone resin added or to additionally use inorganic fillers such as aluminum hydroxide, halogens or phosphorus compounds.
In most systems with silicone resins added, the amount of silicone resin added must be increased in order to achieve satisfactory flame retardant effect, but at the sacrifice of the moldability and mechanical strength of resin compositions. Efforts have been made on silicone resin additives having greater flame retardant effect or additives capable of cooperating with silicone resins to improve the flame retardant effect.
JP-A 176425/1996 discloses a flame retardant resin composition comprising a polycarbonate resin, an epoxy-bearing organopolysiloxane, and an alkali metal salt of an organic sulfonic acid. JP-A 176427/1996 discloses a flame retardant resin composition comprising a polycarbonate resin, a polycarbonate resin modified with a phenolic hydroxyl-bearing organopolysiloxane, and an organic alkali metal salt. Further, JP-A 169914/1997 discloses a composition wherein a petroleum heavy oil or pitch is combined with a silicone compound for improving flame retardance. These silicone resins having special organic functional radicals are expensive because of the complication of their preparation process, but do not achieve a sufficient flame retardant effect to compensate for the increased cost. In this regard, a further improvement is desired.
Also for improving the thermal oxidation resistance of polycarbonate resins, it is known effective to add a silicone resin having alkoxy functional radicals which can be introduced at a relative low cost. JP-A 102352/1979 discloses a thermoplastic resin composition having added thereto a silicone resin containing alkoxy radicals as shown below. ##STR1##
In general, siloxanes having a greater alkoxy content tend to form a network and provide a greater thermal oxidation resistance. The former silicone resin provides insufficient flame retardance because of the lack of phenyl radicals. The latter phenyl-bearing, low molecular weight organosiloxane is also insufficient in flame retardance because of a substantial loss of effective components through gasification by heat during melt processing or combustion.
JP-A 306265/1994 discloses a flame retardant polycarbonate resin composition comprising an aromatic polycarbonate, an alkali or alkaline earth metal salt of perfluoroalkanesulfonic acid, and an organic siloxane resin having alkoxy, phenyl and vinyl radicals introduced therein. The organic siloxane resins used in practice are insufficiently flame retardant because of a low proportion of phenyl among organic substituents. Allegedly, flame retardance is difficult to achieve unless the alkali or alkaline earth metal salt of perfluoroalkanesulfonic acid is blended.